Model of hydrogenated amorphous silicon and its electronic structure

Holender, J. M.; Morgan, G J; Jones, R.

doi:10.1103/physrevb.47.3991

Cited by 39 publications

(22 citation statements)

References 14 publications

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“…The books of Joannopoulus and Lucovsky 16,17 and Street 22 present a good overview of the theoretical and experimental properties of a-Si:H. On account of the technical importance of a-Si:H numerous theoretical investigations have been performed to understand the role of hydrogen in the amorphous state. [23][24][25][26][27][28][29][30][31][32][33] Compared to a-Si the defect concentration in a-Si:H is drastically reduced. It has been observed experimentally that only one out of 10 7 atoms shows a coordination number different from four for a concentration of 20 at.…”

Section: Introductionmentioning

confidence: 99%

Defects ina−Sianda−Si:H: A numerical study

1998

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We present a numerical study of the electronic properties of various structural models of amorphous silicon and hydrogenated amorphous silicon. Starting from an ideal random network, dangling bonds, floating bonds, double bonds, microvoids, hydrogenated dangling bonds, and hydrogenated floating bonds are introduced. The concentrations of these defects can be varied independently, the amount of disorder introduced to the system is therefore strictly controllable. Two continuous random networks, the vacancy model of Duffy, Boudreaux, and Polk and the bond switching model of Wooten, Winer, and Weaire ͑WWW model͒ are investigated. For the relaxation of the structures the potentials of Keating and of Stillinger and Weber are employed. The electronic structure is described by a tight-binding Hamiltonian; the localized or extended character of the eigenstates is investigated via a scaling approach. The vacancy model shows a band gap for small defect concentrations but this fills up with increasing disorder. Similar behavior is found for the case of the other models. In general defects introduce states into the gap region of a-Si, where the dangling bonds lead to the largest density of states in the gap region for a given defect concentration. This model turns out to be unique. For small system sizes an impurity band results that dramatically changes its character for large systems above 4000 atoms to a nearly uniform density of states as observed experimentally. In a-Si:H the dangling and floating bonds are removed and a mobility gap results with a width in good agreement with experiment. The experimentally observed tailing of the band into the gap region ͑first linear, then exponential͒ is well described only for the a-Si:H model derived from the vacancy model and for very large system sizes above 4000 atoms. The WWW model does not lead to this tail behavior. Localized states are found at all band edges but states at the bottom of the conduction band are more strongly localized than those at the top of the valence band.

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Section: Introductionmentioning

confidence: 99%

Defects ina−Sianda−Si:H: A numerical study

1998

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“…[13]. The initial size of the model is 500 atoms, which is then hydrogenated following a method similar to but not identical to Holender and Morgan [14]. In our scheme, the dangling bonds are passivated by introducing H atoms in the RMC-generated continuous random network.…”

Section: Applications: Glassy Gese 2 and A-si:hmentioning

confidence: 99%

Inverse approach to atomistic modeling: Applications to a-Si:H and g-GeSe2

Biswas

Drabold

2008

Journal of Non-Crystalline Solids

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We discuss an inverse approach for atomistic modeling of glassy materials. The focus is on structural modeling and electronic properties of hydrogenated amorphous silicon and glassy GeSe 2 alloy. The work is based upon a new approach 'experimentally constrained molecular relaxation (ECMR)'. Unlike conventional approaches (such as molecular dynamics (MD) and Monte Carlo simulations(MC), where a potential function is specified and the system evolves either deterministically (MD) or stochastically (MC), we develop a novel scheme to model structural configurations using experimental data in association with density functional calculations. We have applied this approach to model hydrogenated amorphous silicon and glassy GeSe 2 . The electronic and structural properties of these models are compared with experimental data and models obtained from conventional molecular dynamics simulation.

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“…Using the resulting atomic coordinates of the simulated a-Si structure, hydrogen was selectively incorporated into the network at three-and fivefold sites using the static algorithm of [21], to obtain hydrogenated amorphous silicon (a-Si:H). For the simulations reported here, the number of hydrogen atoms N H was set to 52, 86, 138, 173, 225, 259, 311, 346, 397 and 432 in each case, and the corresponding number of silicon atoms N Si was reduced to 1676, 1642, 1590, 1555, 1503, 1469, 1417, 1382, 1331 and 1296, respectively.…”

Section: Structure Set-upmentioning

confidence: 99%

Computer simulation of the influence of hydrogen on stress–order correlations in amorphous silicon

Ukpong

2009

Molecular Simulation

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This paper reports the computational simulation of the correlations between atomic-level stress and local structure fluctuations in a computational model of amorphous silicon. A single parameter has been identified, which uniquely characterises the structural order in these structures. This parameter is the linear combination of the SDs of the first and second nearest neighbour separations. The stress fluctuations, under progressive hydrogen incorporation, show two clear dependences on this parameter, and therefore on the structural order. This dual dependency clearly alludes to structural network configurations that contain low and high hydrogen concentrations. The implications of the results on the local geometry of tetrahedrally bonded amorphous solids are discussed.

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Model of hydrogenated amorphous silicon and its electronic structure

Cited by 39 publications

References 14 publications

Defects ina−Sianda−Si:H: A numerical study

Defects ina−Sianda−Si:H: A numerical study

Inverse approach to atomistic modeling: Applications to a-Si:H and g-GeSe2

Computer simulation of the influence of hydrogen on stress–order correlations in amorphous silicon

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